1. Field of the Invention
The present invention relates to the field of portable computer systems, such as personal digital assistants or palmtop computer systems. Specifically, embodiments of the present invention relate to a portable computer system equipped with a dynamic brightness range control to maximize readability in various ambient lighting conditions and to prolong the lifetime of the display, the light and the battery.
2. Related Art
A portable computer system, such as a personal digital assistant (PDA) or palmtop, is an electronic device that is small enough to be held in the hand of a user and is thus “palm-sized.” By virtue of their size, portable computer systems are lightweight and so are exceptionally portable and convenient. These portable computer systems are generally contained in a housing constructed of conventional materials such as rigid plastics or metals.
Portable computer systems are generally powered using either rechargeable or disposable batteries. Because of the desire to reduce the size and weight of the portable computer system to the extent practical, smaller batteries are used. Thus, power conservation in portable computer systems is an important consideration in order to reduce the frequency at which the batteries either need to be recharged or replaced. Consequently, the portable computer system is placed into a low power mode (e.g., a sleep mode or deep sleep mode) when it is not actively performing a particular function or operation.
There are many other similar types of intelligent devices (having a processor and a memory, for example) that are sized in the range of laptops and palmtops, but have different capabilities and applications. Video game systems, cell phones, pagers and other such devices are examples of other types of portable or hand-held systems and devices in common use.
These systems, and others like them, have in common some type of screen for displaying images as part of a user interface. Many different kinds of screens can be used, such as liquid crystal displays, and field emission displays or other types of flat screen displays. Refer to FIGS. 1A–1D for examples of types of display screens.
As illustrated in FIG. 1A, a reflective display is shown including a display screen 110 having a reflective surface 130 so that the display is enhanced in bright external light 103 such as sunlight but requires a front light 120 in darker environments. The display screen 150 of FIG. 1B can also be transflective. It has a reflector 160 to reflect light from an external source 103. This reflector 160 comprises holes 170 through which light from the backlight 140 can pass for lighting darker environments. FIG. 1C illustrates another type of display screen which is transmissive. The transmissive display screen 101 has no reflector so it requires a backlight 102. When bright external light, such as sunlight, is present, this external light 103 competes with the backlight and it becomes difficult to see the transmissive display screen. Another non-reflective type of display is the emissive display screen as illustrated in FIG. 1D. Among the family of emissive display screens one finds Organic Light Emitting Diode (OLED), Organic Electro-Luminescent (OEL), Polymer Light Emitting Diode (Poly LED), and Field Emission Displays (FED). The emissive screen 190 contains light emitting elements and, therefore, requires no separate backlight. As with the transmissive screens, bright external light competes with the emitted light of the emissive display screen. Emissive and transmissive displays can not be viewed very well in the sun unless the brightness is turned very high. High brightness can reduce the life of the display and cause poor battery life performance.
One conventional approach to adjusting the brightness of the display with respect to the ambient light is to include photo detectors to adjust the brightness or to turn a backlight on or off. In this approach there is a fixed brightness range which does not always provide a comfortable viewing experience for the user.
Another conventional approach gives the user manual control of the amount of light being produced for the transmissive and emissive display screens. This approach is satisfactory for conscientious users who regularly monitor the brightness settings and manually adjust them accordingly. However, as is often the case, the user can set the display screen for maximum brightness so that the display is more easily read in sunlight, thereby not having to make frequent adjustments. In the case of the transmissive display, this frequently results in less than optimal battery and backlight lifetime experience. In the case of the emissive display, in addition to a reduced battery experience, the emissive material, usually either an organic or polymer, has a finite lifetime. This lifetime becomes severely shortened if the display screen is always turned to the maximum setting.